Approximately 4,000 Rwandan soldiers have entered the Democratic Republic of Congo since Tuesday as part of a joint Congolese-Rwandan effort to rout Rwandan Hutu rebels of the Democratic Forces for the Liberation of Rwanda (FDLR), Agence France-Presse reports. The Hutu rebels escaped to Congo after participating in the genocide of Rwandan Tutsis and moderate Hutus in 1994, and have generated conflict in the country ever since. According to AFP, an estimated 6,000 FDLR fighters are believed to be in the region.

Congolese authorities have claimed that the current mission would last 10 to 15 days, but The Christian Science Monitor suggests that the campaign will probably take much longer and result in a large number of civilian casualties because of the FDLR’s tendency to use guerilla tactics.

Guillaume Lacaille, a Congo expert at the International Crisis Group, also tells the Monitor that the profitable mines and resources in the region could entice the Rwandan forces to stay longer. “When you consider the natural resources in this territory," says Lacaille, “it is difficult to withdraw without guarantees that one will continue to benefit from those resources.”

In pursuit of the FDLR rebels, government forces have entered the territory of a Congolese Tutsi rebel group, the National Congress for the Defense of the People (CNDP). Until recently, the faction was led by former Congolese General Laurent Nkunda, who rebelled against the government in 2004 because the Congolese army was loath to vigorously pursue the FDLR. According to MSNBC, “In the latest outbreak of violence, rebels led by Nkunda launched an offensive in late August … driving more than a quarter of a million people from their homes.”

But last Friday, several of Nkunda’s top commanders announced an alliance with the Rwandan-Congolese force in the campaign against the FDLR, reports AFP.

The Monitor indicates that General Bosco Ntaganda, Nkunda’s former chief of staff, is actually the new leader of the CNDP. Nkunda and Ntaganda drifted apart after “Ntaganda’s massacre of civilians in December in the Congolese village of Kiwanja.” Ntaganda has been accused of war crimes by the International Criminal Court (ICC), and the United Nations would face a moral dilemma if it sent peacekeeping forces into the conflict.

“This man is wanted by the ICC,” Anneke van Woudenberg, a Congo specialist with Human Rights Watch, told the Monitor. “Congo is under obligation to arrest Ntaganda, not cooperate with him.”

Rwandan Hutus escaped to Congo in 1994 after the genocide; by 1996, their leaders had initiated cross-border attacks into Rwanda against Tutsis. In response, Rwanda invaded Congo in 1996 and again in 1998 to seek out members of the FDLR. Rwandan forces marched on Kinshasa, the capital of Congo, and installed Laurent Kabila as president in 1997.

Kabila ejected the Rwandan Tutsis in 1998 in order to “prove his independence,” according to MSNBC. A few days later, Rwanda and Uganda launched an offensive against Congo in a “war that drew in half a dozen African nations and lasted until 2002.”

Congo created a unity government after 2002 that incorporated rebels into positions of leadership. In 2006, Laurent Kabila’s son Joseph won the presidential elections.

According to the BBC, the Tutsi minority held power over the Hutu majority until 1959, when 200,000 Tutsis fled the country because of civil war. Since then, there have been several incidences of Hutus killing Tutsis on a wide scale, with the largest massacre occurring in 1994.

On April 6, 1994, a plane crash killed Rwandan president Juvenal Habyarimana and Burundi leader Cyprien Ntaryamira, sparking assassination rumors and setting off deadly ethnic violence. Violence quickly erupted in Rwanda; Hutus began attacking Tutsis, despite the presence of a 2,400-member UN peacekeeping force. According to PBS, the next 100 days saw the fastest rate of mass killings in the 20th century, with some 800,000 people murdered. About two million Hutus fled to Zaire, which would become the Democratic Republic of Congo.